Trimaran - Especially Searunner - Owners

[Buzzman]

Jim Brown outlines one method of making a 'fuse' for the Searunner mainsheet in his book The Case for the Multihull. Something similar might work for the C/B..?


From memory, it involved a hasp and staple latch mechanism, with the mainsheet cam cleat attached to it. Rubber bungies were then attached to this such that, in the event of a heavy gust hitting the main, the force on the cam cleat would pull against the bungies, so the upper pasrt of the hasp latch would open, and in that position the sheet would no longer hol in the cam cleat and it would pop out, releasing the tension on the main sheet.


Perhaps something like this could help?

[fgd3]

Originally Posted by Roy M

I previously rebuilt my centerboard and am considering an alternative mounting system. In the past I used nylon parachute cord, 500# test, as a fuse to release the board when (NOT, IF) I hit something at speed. It worked okay, but it was a hassle resetting a new fuse. I'm hoping to create a self adjusting shock absorber that will take the hit, but give a bit so as to reduce the sudden impact of collision.

Gemini catamarans use a lock nut to tighten the centerboard drum. The line is wound in such a way that when the board collides with something the drum rotates to loosen the lock nut. Once the obstruction is cleared, readjust the centerboard and retighten the lock nut. The Gemini control lines are used to raise and lower the centerboard so both ends are attached to the centerboard and wound around the drum. Turn the drum clockwise to raise the board, counterclockwise to lower it.


If all you need is a line to hold the centerboard down it would be easier to rig a drum with a lock nut than the system on the Gemini.

[Cadence]

Originally Posted by fgd3

Gemini catamarans use a lock nut to tighten the centerboard drum. The line is wound in such a way that when the board collides with something the drum rotates to loosen the lock nut. Once the obstruction is cleared, readjust the centerboard and retighten the lock nut. The Gemini control lines are used to raise and lower the centerboard so both ends are attached to the centerboard and wound around the drum. Turn the drum clockwise to raise the board, counterclockwise to lower it.


If all you need is a line to hold the centerboard down it would be easier to rig a drum with a lock nut than the system on the Gemini.

A piece of string tied to the CB line and lashed off works. Not sophisticated but works.

[Tusitala]

On our 34 there's a figure 8 knot in the centerboard line where it exits the trunk just below the mast base. There's a piece of light line bowlined thru the figure 8. we pull the board down with the centerboard line and use the light line as the hold down line. it just pops if we hit anything hard enough and it's location makes it really easy to replace occasionally.

Pat

[Constant Camber]

I have a constant camber 40 which is equivalent to Brown 37. I want to replace an inboard Diesel 30 hp with twin high thrust outboards. How much horsepower with each one need to move 10,000 pounds against 20 wind?

[Roy M]

Two outboards, in twenty knot wind, will probably be spending an uncomfortable amount of time out of the water revving futilely. And being gas engines, will use a lot of fuel. Plus the weight of the engines and mounts, and the hassle of performing service in an awkward location, possibly in rough conditions. The thirty horse engine, if an inboard Yanmar, would weigh about three hundred pounds and be located inside the hull, closer to the center of the boat, and easier to service, especially when things are lumpy or at night.

In 1989 I crewed on YANMAR ENDEAVOR, a composite trimaran with no sails, designed by Gino Morello, and powered by twin DIESEL outboards. We established the record of nine days from San Francisco to Oahu, burning about 400 gallons of diesel. It was meant to showcase these heavy outboards as possible alternative power. It wasn't much fun. I don't think the gas engines would have been successful under Transpac conditions.

[Buzzman]

It depends. Some smaller capacity motors have Hi Thrust gear boxes and larger diam props to provide higher thrust, such as Yamaha 9.9 T9 High Thrust. Two of these would be more than enough, but one might be sufficient.
Bear in mind that David Lewis, first catamaran circumnavigator in Prout 40 Rehu Moana in the early Sixties did so with only a British Seagull 102 Series 5HP Hi Thrust motor.
It's also advisable to get long shaft motors so as to keep the prop immersed in rougher seas, and reduce ventilation.
https://www.yamaha-motor.com.au/prod...ur-stroke/t9.9
The trick when mounitng twin outboars to a tri or cat is to mount them on or in front of the aft beam, so as to minimise the propensity fot he props coing out of the water.
One way to achieve this is wells in the wing, with a vertical sliding mount system.
Another option is to build small v-shaped pontoons, pivoting at the forward end where attached under the wing, thus enabling the motors to ba firmly attached ot the small pontoon, yet float up and down with the swell, thereby enabling short shaft motors to be utilised. These are usually MUCH cheaper than long shaft versions.
Two 2nd hand 15HP shorties would be the 'shoestring' option in this case.

[Cavalier MK2]

The Vagabond is probably about the mass of a SR 34. One 9.9 Yamaha high thrust can push it into 20 knots+ with corresponding seas. 2 of those would be plenty. Sleds add some weight though, I'd think about one 15 or 20. With exhaust, mount, shafting etc.. that diesel is likely we'll past 300 pounds so add it up to compare one or 2 outboards.

[Constant Camber]

Thanks for all the info supplied so far. I have drawings for making sleds and perhaps using 9.9 high thrust Yamaha‘s. However how would one mount The dual controls and run the cabling from the center cockpit to both sides of the Aft bulkheads?

[Cadence]

Originally Posted by Constant Camber

I have a constant camber 40 which is equivalent to Brown 37. I want to replace an inboard Diesel 30 hp with twin high thrust outboards. How much horsepower with each one need to move 10,000 pounds against 20 wind?

A couple of 15HP four strokes should do you. I had a Honda with a 28"leg. Pushed an SR31 at 7.5K on .75gph on calm water.

[Cavalier MK2]

For the controls, etc.... the choices are of course over, under or through, if you are not familiar with OB installations you may want to consult. For sure sled attachments have to be secure in heavy weather, think of the engine at the end of the arms being subject to abrupt wave movement while on full thrust. I'd suggest contacting John Marples, a friendly fellow, for suggestions on the structure.

[Roy M]

Status report: I keep imagining I'm approaching the end of sanding the cabinsides. It's a fantasy, but things are getting better. The problem is, again, sequences. In order to keep up the rhythm of progress, I need to order stuff in advance of when I need it. Covid brought with it the insecurity of delivery, accessibility, and inventory, cutely named supply chain. For example, I used Bomar 10 by 10 hatches to ventilate the galley, one over the galley stove, one over the sink, and a third mounted through the curved aft panel aft of the sink. Covid spelled the end of a lot of products, Bomar, apparently one of them. I had removed them, and, being forty years old, I thought I'd disassemble them, replace the polycarbonate lens, and re anodize the frames. Alas, no anodizing facilities have survived in California. But, fortunately, Lewmar still has it's Ocean 10 series with flanges, only a slightly larger opening required. And considering the hassle of disassembly, producing new lenses, having to sandblast, prime and paint the originals, buying new ones didn't sting as much. Plus, the Lewmars are superior. But I still have to modify the cabintop before painting, so.... more details before I paint the cabinsides and cabintop. The good part is that things look better and better.

Another odd thing about change is that sometimes things work out better. For example, my galley stove project. Several years ago I decided to fabricate a custom stove and oven unit. Previously, I had always used Magic Chef RV stove units that had an oven ABOVE the range burners. Cheaply made using steel, these units lasted about ten or fifteen years before rusting out from boiling seawater on the stove. Then, they magically disappeared from existence. I had bought a Force 10 and radically chopped and welded a new variation. Then I discovered I couldn't get a thermostat and oven valve to work with the newly configured Frankenstein 10. Bummer! Then, I learned that Force 10 had formed a partnership with a French manufacturer called ENO which produces SEPARATE countertop burner units and an independent oven. Wow! It even works far better, allowing me to gain valuable storage in a drawer behind the stove, where I will be able to store pots, pans and lids securely and easily accessed.

So, one door closes, and another opens. Things are moving forward, and with improved efficiency and beauty. Very cool. Pictures will be forthcoming, AFTER I'M DONE WITH THE DAMN PAINTING. [emoji4]

[longjonsilver]

Things are moving forward, and with improved efficiency and beauty. Very cool. Pictures will be forthcoming, AFTER I'M DONE WITH THE DAMN PAINTING. [emoji4]

Were cheering for you Roy

[Roy M]

Thanks! It's kind of like the last few months when I was building the boat. Some things just seemed to move at a snail's pace.

[Constant Camber]

Hypothetical question
I checked out that seawind catamaran which has a 14,000 lbs displacement and is being powered by twin Yamaha 9.9 High thrust outboards. Plans to switch from diesel and mounting each one one a pivoting sled with Engine motors Just behind the aft bulkhead. The question is how much would the outboards do to value of the value of the boat instead of an inboard?